template<class T> class Array {
T* v;
int sz;
public:
explicit Array(int);
T& operator[](int);
T& elem(int i) { return v[i]; }
};
Array<int> v1(20);
typedef std::complex<double> dcomplex; // std::complex is a standard library template
Array<dcomplex> v2(30);
Array<dcomplex> v3(40);
void bar() {
v1[3] = 7;
v2[3] = v3.elem(4) = dcomplex(7,8);
} — end example
template<class T> void f();
template<int I> void f();
void g() {
f<int()>(); // int() is a type-id: call the first f()
} — end example
template<class T> class X {
static T t;
};
class Y {
private:
struct S { /* ... */ };
X<S> x; // OK: S is accessible
// X<Y::S> has a static member of type Y::S
// OK: even though Y::S is private
};
X<Y::S> y; // error: S not accessible
— end example
template <template <class TT> class T> class A {
typename T<int>::S s;
};
template <class U> class B {
private:
struct S { /* ... */ };
};
A<B> b; // ill-formed: A has no access to B::S
— end exampletemplate<class T = char> class String; String<>* p; // OK: String<char> String* q; // syntax error template<class ... Elements> class Tuple; Tuple<>* t; // OK: Elements is empty Tuple* u; // syntax error— end example
template<class T> struct A {
~A();
};
void f(A<int>* p, A<int>* q) {
p->A<int>::~A(); // OK: destructor call
q->A<int>::~A<int>(); // OK: destructor call
} — end example
template <class T> class X { };
template <class T> void f(T t) { }
struct { } unnamed_obj;
void f() {
struct A { };
enum { e1 };
typedef struct { } B;
B b;
X<A> x1; // OK
X<A*> x2; // OK
X<B> x3; // OK
f(e1); // OK
f(unnamed_obj); // OK
f(b); // OK
} — end example
template<const int* pci> struct X { /* ... */ };
int ai[10];
X<ai> xi; // array to pointer and qualification conversions
struct Y { /* ... */ };
template<const Y& b> struct Z { /* ... */ };
Y y;
Z<y> z; // no conversion, but note extra cv-qualification
template<int (&pa)[5]> struct W { /* ... */ };
int b[5];
W<b> w; // no conversion
void f(char);
void f(int);
template<void (*pf)(int)> struct A { /* ... */ };
A<&f> a; // selects f(int)
template<auto n> struct B { /* ... */ };
B<5> b1; // OK: template parameter type is int
B<'a'> b2; // OK: template parameter type is char
B<2.5> b3; // error: template parameter type cannot be double
— end example
template<int* p> class X { };
int a[10];
struct S { int m; static int s; } s;
X<&a[2]> x3; // error: address of array element
X<&s.m> x4; // error: address of non-static member
X<&s.s> x5; // OK: address of static member
X<&S::s> x6; // OK: address of static member
— end example
template<const int& CRI> struct B { /* ... */ };
B<1> b2; // error: temporary would be required for template argument
int c = 1;
B<c> b1; // OK
— end example
template<class T> class A { // primary template
int x;
};
template<class T> class A<T*> { // partial specialization
long x;
};
template<template<class U> class V> class C {
V<int> y;
V<int*> z;
};
C<A> c; // V<int> within C<A> uses the primary template, so c.y.x has type int
// V<int*> within C<A> uses the partial specialization, so c.z.x has type long
— end example
template<class T> class A { /* ... */ };
template<class T, class U = T> class B { /* ... */ };
template<class ... Types> class C { /* ... */ };
template<auto n> class D { /* ... */ };
template<template<class> class P> class X { /* ... */ };
template<template<class ...> class Q> class Y { /* ... */ };
template<template<int> class R> class Z { /* ... */ };
X<A> xa; // OK
X<B> xb; // OK
X<C> xc; // OK
Y<A> ya; // OK
Y<B> yb; // OK
Y<C> yc; // OK
Z<D> zd; // OK
— end example
template <class T> struct eval;
template <template <class, class...> class TT, class T1, class... Rest>
struct eval<TT<T1, Rest...>> { };
template <class T1> struct A;
template <class T1, class T2> struct B;
template <int N> struct C;
template <class T1, int N> struct D;
template <class T1, class T2, int N = 17> struct E;
eval<A<int>> eA; // OK: matches partial specialization of eval
eval<B<int, float>> eB; // OK: matches partial specialization of eval
eval<C<17>> eC; // error: C does not match TT in partial specialization
eval<D<int, 17>> eD; // error: D does not match TT in partial specialization
eval<E<int, float>> eE; // error: E does not match TT in partial specialization
— end example